There is an increasing demand for organic polymer or thermoplastic fibers of small diameter, often referred to as microfibers, for a variety of uses, such as, for example, in the manufacture of filter media or sorbent material. A preferred method of producing such fibers is by a rotary process whereby molten polymer is fed to a spinning disc containing a myriad of small holes through which the material flows by reason of centrifugal force. The rotary method not only enables large quantities of fiber to be produced at a rapid rate, but permits the physical parameters of the fibers to be more readily controlled.
The specific type of rotary process employed can vary greatly. As one example, apparatus is described in U.S. Pat. No. 4,937,020 which utilizes a rotating nozzle head to which molten polymer is introduced under preliminary pressure, and the resulting fibers are additionally drawn by gas streams exiting the nozzle head in the vicinity of the nozzle holes. The nozzle head includes separate passages through which molten polymer and gases flow, each passage including axial and radial components. In addition, heating coils are included for controlling the temperature of the melt at the exit holes. Because the process essentially takes place entirely within the nozzle head, the nozzle head and its various components must be manufactured to extremely demanding tolerances. Thus the cost of the process equipment would tend to be high and the maintenance of the equipment would be difficult.
It would be preferable to utilize a process made up of individual components which are more economical to produce and maintain, yet which enable organic polymer fibers of various parameters to be readily produced at high rates. Further, it would be desirable to be able to produce organic polymer fibers in much the same way as microfibers of glass are produced, to take advantage of proven procedures for manufacturing fibers from molten material at high production rates. Moreover, the equipment employed in the manufacture of glass microfibers is relatively simple in design and is not dependent on self-contained nozzle constructions such as that described in the above-mentioned patent.
Unfortunately, it is not possible to produce satisfactory fibers by simply running molten polymer through rotary fiber glass equipment. A basic reason for this is that the design of equipment used to produce glass microfibers is determined to a large extent by the temperature and physical characteristics of the molten glass. Because the temperature and specific gravity of molten glass are considerably higher than the temperature and specific gravity of molten polymers, the equipment and process parameters used in glass microfiber production cannot be used to produce organic polymer fibers.
It is therefore an object of the invention to provide simplified equipment for the production of organic polymer fibers, utilizing the principles where possible of the basic rotary method of manufacturing glass microfibers.
It will be understood that although the following description refers to the manufacture of fibers primarily from molten organic polymer or thermoplastic resin, the term "organic polymer" is sometimes used to refer to both types of materials. Where appropriate, this term may also be interpreted as including thermosetting resins as well, as explained more fully in the specification.